Method of activating catalytic surfaces



Filed 0st. 3, 1939 Q1 ACTIVATING CATALYTIC SURFACES Patented Apr. 6,1943 OFFICE METHOD OF ACTIVATING CATALYTIC SURFACES Marion H. Gwynn,Mountain Lakes, N. J.

Application October 3, 1939, Serial No. 297,651

4 Claims.

This application is continuation-impart of my copending applicationsSerial No. 130,478 filed March 8, 1937, now Patent Number 2,174,510,granted October 3, 1939, and Serial No. 240,447 filed November 12, 1938.This invention relates to catalysts and to the preparation andreactivation of active metallic type catalytic surfaces, particularlythose adherent or fixed to the underlying metal. These treated surfacesare especially adapted for use in hydrofining, i. e. hydrogenatingand/or refining oils and other organic or carbonaceous compounds. Thesurface layers may also be used as reagents, as for example in theformation of metallic sulphides; or as adsorption or purifying agents,as in the treatment of vegetable or, animal glycerides before steamdeodorization, or as when doctor sweetening light petroleum or likedistillates, or as tower packing or otherwise.

The essential activating step of my invention is an anodic peroxidationin an aqueous alkaline electrolytic bath, preferably containing thehydroxidc of a heavier alkaline earth metal, to pro- "aduce a surfacewhich is catalytic with respect to sulphur sensitive hydrofining withoutfurther chemical treatment. These hydroxide electrolytes may be used inextraordinarily low concen-- trations. Anodic oxidation on metals usingsalts as electrolytes together with a subsequent reduction in hydrogenbefore use has been proposed for the production of active precipitatedmetallic catalysts. However either powder or fixed catalyst so preparedfails to maintain its activity substantially uniform during hydrofining.During electrolysis, salt electrolytes readily change in composition,and also allow sulphate ion to accumulate in the electrolyte and henceare impractical for the removal of sulphur from fixed metal surfaceswithout removing catalytic metal itself. Moreover I find that salts aregenerally deleterious in the electrolyte, increasing polarization andexerting a depressive effect On the adherence and activity of thecatalyst anodically oxidized in their presence.

I also find that oxidizing treatments prior to my anodic per-oxidationimprove the activation, particularly when activating cobalt or nickelsurfaces. The preferred form of my invention comprises activating orperoxidizing a metallic surface previously subjected to an oxidizingtreatmenl, in an anodic peroxidation bath as described. For example Imay prepare highly active black fixed catalytic surfaces or surfacelayers by preliminarily treating a metal such as cobalt or nickel in aforaminate state to form a hydrated and/or a moderately catalyticsurface layer. This pre-treatment may be effected by anodic oxidationanddeposition in an alkaline bath or by anodic activation in an acid bath,particularly on cobalt, or by other chemical means.

The surface comprising this hydrated or moderately catalytic layer isthen rendered further catalytic and is peroxidized at the anode in anelectrolytic bath which contains a substantially saturated and unheatedaqueous solution of a hydroxide of a metal selected from the groupcontaining calcium, strontium, and barium. The catalyst produced in thisway without further chemical treatment is highly catalytic and ready foruse in sulphur sensitive hydrofining operations, and may maintain itsactivity substantially uniform during hydrofining until spent. Thiscatalyst is not a precipitate, but is substantially integral with metalbeneath the catalytic layer. Instead of starting with a new metalsurface I may start with catalyst which has been used, for instance'asulphur bearing surface layer may be anodically desulphurized andactivated without loss of metal from the surface, since the sulphur isreacted with the electrolyte and precipitated out of solution as aninsoluble sulphate.

Salts, whether or not forming soluble compounds with the catalyticmetal, are tolerated to a limited extent and may be present in myalkaline electrolytic bath, provided that hydroxyl is the predominantion in the anolyte. Thus when a fixed and sulphided surface of a metalis anodically activated in an alkaline solution other than strontiumhydroxide or barium hydroxide, sulphate ion may accumulate in solutionand dissolve catalytic metal when the sulphate and other salt anions arepredominant over hydroxyl ion in the anolyte. If anions other thanhydroxyl are present in my alkaline electrolytic bath, they should notpredominate in the anolyte. For in stance, when a fixed and sulphidedsurface of a metal is anodically activated in an aqueous solution ofcalcium hydroxide, the solution is preferably changed before thesulphate ion exceeds the hydroxyl ion in concentration and activity inthe anolyte, on account of the solubility of calcium sulphate.

I mayalso use as anodic peroxidation electrolytes soluble alkalinehydroxide solutions similarly low in thermodynamic activity to thesolutions of the hydroxide of calcium, strontium, barium. For example Imay also use a cool one normal solution of lithium hydroxide. Generally,however, the alkali metal hydroxides appear incapable of anodicperoxidation. It is my belief that this is due to their highthermodynamic activity coefficients.

I may employ my alkaline electrolytic activation substantially withoutother chemical treatment, particularly for the activation of the lessercatalytic and hydrogenating metals such as lead or tin or copper orsilver, which however are catalytic for desulphurization rather thanhydrogenation.

My invention is not limited to lead or tin or cobalt or nickel or copperor silver, which as a group are remarkably desulphurizing and reacti--vatable, but may be applied to other metals, including alloys comprisingone of the above elements or alloys similar to cobalt or nickel,ferromagnetically similar, for example. The catalytic surfaces resultingfrom my anodic peroxidation, particularly those black in color, appearto possess a crystal lattice parameter substantially longer than that ofthe normal oxide. It is withimt/he contemplation of the invention toactivate metal of face center cubic crystal lattice, neither extremelyelectropositive nor electronegative, especially those which in theactivated state are catalytic for the following vapor phase tripledecomposition between 200 C. and 300 C. or like reaction:

R is olefinic and M is a metallic element or mixture and x is specificwithin limits for each metal, varying for example from about 1 for leadand 1.2 to 1.5 for the more active metals such as cobalt and nickel, tobetween 1.6 and 2 for copper and silver.

Peroxidation appears naturally adapted to the reactivation ofdesulphurizing surfaces, since oxygen and sulphur are elements of thesame -periodic family and since Oz has the same molecular weight as S1.Sulphides of these peroxidiz able catalytic metals are black, and thesurfaces activated by .my anodic peroxidation are also preferably blackin color. Of the several peroxidizable metals, three are'particularlyrelated and active and useful when activated as. described herein.Thesethree are nickel and the two elements of adjacent atomic number,cobalt and copper.

Catalytic surfaces prepared and deactivated with use as described in mycopending application, Serial No. 130,478, may be reactivated by a.process comprising my anodic peroxidation. Likewise the catalysts hereindisclosed may be used in the desulphurization of organic compounds asset forth in my U. S. Patent 2,073,578 or in my corpending application,Serial No. 130,478., new U. S. Patent 2,174,510. The values of a: in Mrabove are related to the original activity of the catalyst and to themanner in which I may carry out that desulphurization. Desulphurizationof organic compounds by these catalysts is preferably accompanied byhydrogenation, particularly replacing the sulphur with hydrogen. Theorganic sulphur compounds are preferably in hydrocarbon solution as withcrude motor fuels. MIS is readily reconverted electrolytically toMrO2-2H2O or like compound by my invention as described herein.

In the drawing:

Fig. 1 represents a perspective view of an assembly of screen discs;

Fig. 2 represents a diagrammatic view showing 75 the relative positionsof a disc or other assembly and a cathode disc;

Fig. 3 represents a perspective view of another form of assembly; and

Fig. 4 represents a diagrammatic showing of apparatus for the continuousanodic activating assemblies and for replenishing the electrolyte.

I will now give some examples ofhow my invention is to be practiced, butI am not to be limited thereto, as they may be modified in manyparticulars without departing from the spirit of the invention. Beforechemical activation, but not reactivation, each assembly may bephysically treated to increase the initial foraminate charactor of theassembly, as described near the end of specification. The resultingactivated surfaces have general as well as specific usage.

Example I The assembly 10 is composed of several cobalt or cobalt coatedscreens designated by the reference numeral l2. These screens are 12.7cm. in diameter fastened together so that their centers lie along astraight line to form a disc assembly as shown in Fig. 1. The diameterof each Wife of the screen is about 0.04 and the adjacent parallel wiresare 0.24 cm. apart on centers. This disc assembly I!) is placed in abath with its principal plane parallel to a flat circular nickel sheetcathode 14 also 12.7 cm. in diameter as shown in Fig. 2. The bath (notshown) contains an electrolyte composed of commercial water glass atabout 35 C. and a current density of about 8 milliamperes per sq. cm.and 4.6 volts are applied for sufficient time to form on the surface ofthe screens a deep blue coating containing hydrated silicate which is adehydration promoter. This is a preliminary oxidizing treatment.

The screens are withdrawn from the water glass bath and the excesssilicate and deposited hydrated silica may be removed with an aqueoussolution of half normal sodium hydroxide at, about 60 C., at the sametime converting part of the cobalt silicate to cobalt hydroxide. Thescreen surfaces are then given a further anodir: activation in anotheraqueous bath containing calcium hydroxide saturated at 5 C. Sufficientvoltage is impressed on the calcium hydroxide bath to maintain a currentdensity of about 5 milliamperes per sq. cm., and this is continued forabout one quarter hour or until the current efiiciency substantiallydiminishes. The screens are then withdrawn and washed, being catalyticwithout further treatment. Other alkaline electrolytes depositing adehydration promoter in the surface layer may be substituted for thewater glass, particularly those which are concentrated and colloidal andwhich gel on the slight addition of acid.

Example II A new cobalt assembly of the same internal and external shapeand size as described in Example I is highly peroxidized in thefollowing manner. The assembly is connected as the anode and pretreatedin an electrolyte composed of 4 normal aqueous hydrofluoric acid at 5 C.The cathode and its placement are also as described in Example I. Thecurrent density and voltage are adjusted to form a deep adherent blacklayer on the cobalt assembly. About 4 volts are first applied, or avoltage sufiicient to produce a current density on the order of 30milliamperes per sq. cm., and when after a few minutes the currentdensity or current efficiency diminishes, the potential may be increasedcontinuously or at intervals t about volts or higher. When the currentefficiency substantially decreases or when a deep black surface layer isformed, the hydrofluoric acid is withdrawn from the bath, and thetreated cobalt assembly is drained and washed. A new electrolytic bathis then run in composed of about 0.04 normal solution of calciumhydroxide at 5 C., which is a nearly saturated solution. A currentdensity of about 3 or 4 milliamperes per sq. cm. and a voltage of 4.6 isapplied for several minutes or until the fluorine is displaced from thesurface.

All steps in my invention may be electrolytic, for instance in ExampleII washing when used may be facilitated by electrodialysis. 1

Other metals may be substituted for cobalt in Example II, for instancean alloy of cobalt containing nickel or palladium. Strontium or bariumhydroxide or milk of lime may be substituted for the calcium hydroxide.Other strong acid electrolytes may be substituted for the hydrofluoricacid, preferably decomposable and in a dilute solution. Such acids withor without impressed electrical potential may be used to treat these andother surfaces prior to my anodic peroxidation.

Hydration of the surface layer prior to my anodic peroxidation may beobtained as in the previous examples, or during reactivation with steamor hypohalites, or by other methods or combinations of methods.

Example III A new copper assembly composed of pure copper turnings whosesuperficial area is about 1,000 sq. cm. is packed in a rectangularboxlike container cm. high and 10 cm. wide, composed of coarse opencopper screening. The assembly is placed in a bath with its 10 cm. by 10cm. faces parallel and opposed to a square sheet nickel cathode also 10cm. by 10 cm. Thus the facial area is 100 sq. cm., identical to the 12.7multiplied by 1%; pi of the circular discs of Fig. 1. The assemblyis'heated for several hours in air at the lowest temperature required toform a dark oxide coating on the entire surface, for instance near 300C. The oxidized turnings and screen are then connected as the anode inan aqueous electrolytic bath containing about 0.5 normal bariumhydroxide at about 30 C. Sufficient voltage is applied to maintain acurrent density of 10 to 20 milliamperes per sq. cm., and when theelectrolytic peroxidation is initiated the cur rent density is loweredsomewhat below 10 milliamperes per sq. cm., and the electrolysiscontinued until the current efficiency substantially diminishes. Thecatalyst is then withdrawn, drained and washed. Should the air oxidizedturnings only respond to the anodic peroxidation to a low degree asnoted by a relatively low early current efficiency, they may be washedand reactivated as follows: Reduce in hydrogen at about 200 0., cool insteam, and then repeat the air oxidation given above, and anodicallytreat as given before.

Pure silver may also be treated in this manner with or withoutpreliminary air oxidations.

Example IV The assembly I6 is composed of several new nickel or nickelcoated screens of the same area, wire and weave as the screens inExample I. The nickel or nickel coated screens l8 are square instead ofcircular however, each 10 cm. x 10 cm., and fastened together on atleast one edge 20 as in a book. The external dimensions are those of theassembly in Example III. The surfaces of the screens are pretreatedseveral hours with the vapors of concentrated nitric acid at 40 C. or 50C. to pit and oxidize the nickel surface to form a nitrate of nickel,and then without washing, the mass is dried and gently heated in acurrent of air above about 200 C. and/or at near the lowest temperaturerequired to evolve fumes and decompose a substantial portion of theresulting nickel nitrate and darken the mass, for instance at about 300C. This assembly, now moderately catalytic, is placed parallel to asquare nickel sheet cathode as given in Example III, in an electrolytecomposed of a one-thirtieth normal aqueous solution of calcium hydroxideat about 15 C., and a voltage of about 4.6 volts applied until a currentof about 2 amperes passes, i. e. a current density of 20 milliamperesper sq. cm. As soon as blackening begins the amperage is reduced toabout 0.4, i. e. a current density of 4 milliamperes per sq. cm., andthe electrolysis continued for at least an hour or until no furtherdarkening is noted or' until the evolution of oxygen approaches one-halfthe volume of the hydrogen. After electrolysis, the solution iswithdrawn from the bath and the screen assembly carefully washed withwater, being catalytic without further treatment.

Other surfaces may be treated with nitric acid prior to my 'anodicperoxidation, for instance a new cobalt surface, or the new coppersurface described in Example III.

Example V The assembly is the peroxidized nickel assembly such asdescribed in Example IV, then nearly used to capacity in adesulphurizing operation such as represented by the chemical equationabove given, and subsequently steamed at least sufficiently to removethe hydrocarbons. This spent assembly is then made the anode in anelectrolyte composed of an aqueous substantially saturated solution ofstrontium hydroxide at room temperature. A current density of 10milliamperes per sq. cm., or as much higher current density as needed toinitiate reactivation is applied for a few minutes, and then the currentdensity is gradually reduced to about 4 or 5 milliamperes per sq. cm.The electrolysis, is continued until most of the sulphur is removed oruntil tests on the electrolyte indicate the cessation of strontiumsulphate formation; Without further chemical treatment, the catalyst maythen be used again, preferably for the same use as before.

Lead tolerates higher sulphate ion concentrations in the electrolytethan the other catalytic metals. Thus I may operate the process asdescribed in Example V, but starting with a cold saturated calciumhydroxide electrolyte, and with lead instead of nickel as the metalliccomponent in the surface layer.

Nickel or copper or like surfaces sulphided by adsorption of heatedorganic sulphur vapors and/or liquids without added hydrogen atrelatively low non-pyrolytic temperatures, may be treated by myinvention, as in Example V. The electrolyte may be replenished bycirculation over solid strontium hydroxide or by the addition of a hotsaturated aqueous solution of strontium hydroxide, first howeverseparating out any precipitated strontium sulphate as by settling orcentrifuging or filtration.

In Fig. 4 I have shown a diagram of an arrangement for continuous anodicperoxidation,

recirculating the electrolyte in contact with a hydroxide such as thestrontium hydroxide as mentioned above. The reference number 22designates the electrolytic tank slightly tilted toward orifice 24 andcontaining the aqueous alkaline earth metal hydroxide electrolyte. Abovethe electrolytic tank is an electrode conveyor 23 for continuouslymoving the electrodes from right to left during anodic peroxidation. Thecatalyst assemblies 28 are connected by metal anode connectors 21 to theconveyors anode bar 29. Between each assembly 28 and parallel theretoare sheet nickel cathodes 30, connected by metal cathode connectors 3|to conveyor's cathode bar 33. The electrodes enter the tank or bath inrelatively spent electrolyte 25, and emerge from a relatively freshelectrolyte 26. Thus the reactivation is countercurrent with respect tospending of the electrolyte. The relatively spent electrolyte 25 passesthrough pipe 32 to a settling tank 35, containing a false bottom 36which may be lifted out by a device 38 together with impure alkalineearth metal sulphate and other solids which have settled out. Thesettling tank has a loose cover 40. The overflow from the settling tankpasses through pipe 42 to a centrifuge 44 and the clarified alkalineearth metal hydroxide passes through pipe 48 to covered tank 48 providedwith vent 50. The centrifuge is provided with means to remove solidmaterial. processed to convert precipitated alkaline earth sulphates tohydroxide electrolyte in apparatus not shown. A pipe 52 leads from thebottom of tank 48 to pump 54 and by means of the pump the liquid ispiped to hydroxide replenishing chamber 58 containing a hydroxide suchas strontium hydroxide in a heated aqueous solution or as theoctahydrate. A substantially saturated hydroxide solution 26 may passfrom chamber 58 through pipe 60 and orifices 62 back to the electrolytictank 22.

Thus a surface layer comprising nickel sulphide and/or sulphate istreated by means of double decomposition between the surface layer andthe electrolyte, preferably adding a hydroxide of either calcium,strontium or barium to the bath during the electrolysis. The resultingprecipitated alkaline earth metal sulphate may be collected andreconverted to hydroxide, as with an alkali of sodium. For instancestrontium sulphate may be autociaved with sodium carbonate solutionforming sodium sulphate, and the resulting strontium carbonate convertedto strontium hydroxide in a current of gas comprising superheated steam.If barium compounds are used instead of those of strontium, the bariumcarbonate generally requires coke and air for its conversion to alkali.Strontium sulphate or barium sulphate may be otherwise converted totheir hydroxides, for instance they may give up their sulphate to acalcium compound forming calcium sulphate.

Or a surface layer substantially a metal sulphide may be desulphided atleast in part prior to anodic activation, e. g. nickel sulphide orcobait sulphide may be strongly heated with an oxygen gas and/or steamto convert most of the sulphides to oxides, then these oxide films maybe further treated until sufficiently hydrated to respond to anodicperoxidation.

The surface layer prepared for my anodic peroxidation may consist of acharacteristically colored salt, and such salts are generally hydrated.

This and the solids from 36 may be If such a salt resists anodicperoxidation, its resistance may be decreased by further treating priorto anodic peroxidation, for instance treating with a strong alkalisolution as given in Example I to change at least a portion of the saltto the hydroxide. I may treat other surfaces, particularly surfacesconsisting of a compound of the catalytic metal other than the sulphide,with heated and/or strong alkalies preliminary to anodic peroxidation.The concentration of said strong alkali is preferably high, but notextreme. If the preliminary surface layers of the more active metals arenot well hydrated, the surface layer should be relatively deep,especially on metals like cobalt. A relatively shallow layer of adherentnickel hydroxide, or a somewhat thicker layer of cobalt hydroxidesuflices to initiate deeper oxidation of the catalytic surfaces with myanodic peroxidation. The surfaces more activated by my invention requirethe more catalytic preliminary surface layer. For instance, the metalswhich are both the more catalytic and form the higher oxides require themore hydrated and/or deeper preliminary layer. The less oxidizable andadherent the layer, the more hydrated and/or deeper is the requiredpreliminary layer.

The peroxidation of the surface layers appears to be quite autocatalyticso long as the chemical potential required for the peroxidation is lessthan about 1 volt. Hence those agencies which initiate peroxidation areuseful, and result in better activation and substantial savings ofcurrent and time. For instance, the more activatable compounds in thesurface or formed on the surfaces by proper pretreatments, during theirperoxidation initiate the peroxidation of the more difiicultlyactivatable compounds or of the underlying metal itself, Non-cotalyticsurface layers containing only a slight amount of hydrated compoundspreferably oxidizable respond to anodic peroxidation. A hydrofiningcatalyst prepared by my invention and substantially but not entirelyspent constitutes such a surface=lay er. Successive reactivations aregenerally; accompanied by increases of depth of a surface layer andreceptivity to the activating treatment, especially when hydrogenatingat low temperatures. My invention is not to be restricted to thetheories expressed herein.

The catalyst may be removed from the hydroflning chamber or the towerfor reactivation or may be reactivated in place when properly insulated.The cathodes may be sheet Monel metad or nickel and treated to lower theovervoltage.

A diaphragm between the electrodes may be provided. The removal ofoxygen from the anode surfaces, especially during the latter stages ofperoxidation, may be facilitated as by imparting motion to the anode oranolyte.

I prefer that the voltage of the peroxidation baths comprising thehydroxides of calcium or strontium or barium be between 4V2 and 6 volts,and that the temperature be maintained below about 50 C. The currentdensity of these and other alkaline electrolytes may be started at acurrent density of 20 milliamperes per sq. cm. of facial area and thendecreased, for instance rapidly at first, slowly at the end. I preferthat these current densities be maintained above 1 milliampere per sq.cm. of facial area, and the average current density below about 10milliamperes per sq. cm. of facial area.

The current density is preferably closely adjusted near the lowestcurrent density at which ,tion of the nickel anode.

relatively high current efficiency canbe obtained, especially during theearlier or intermediate portions of the anodic activation in the lowactivity coefficient electrolytes. However the current density may besufficiently high during the initial stages of the electrolysis toinitiate oxidation without loss of surface. I prefer that the product ofthe current density and current efficiency be decreased during theactivation at the anode, particularly at the extreme portions of theactivation.

' The current may be continued until the current efficiency at constantcurrent density markedly decreases, or until practically no furtherperoxidation occurs, or until a layer of activated oxide covers thesurfaces to a depth of 10 to 10 catalytic metal atoms, for example anaverage depth of 10 catalytic metal atoms, or until the surface ishighly catalytic, or until sufficiently catalytic for active hydrofiningwithout further chemical treatment. The time of electrolysis isproportional to the ratio of the superficial area and the facial area,and is also proportional to the depth or the activated surface layer.

In the foregoing examples, the total superficial area of each assembly,internal and external, is about 100 to 1,000 sq. cm., the facial area ofeach assembly is 100 sq. cm., and the ratio thereof termed th surfacefacial ratio, is about 1 to 10. The screens may be extended in lengthand/or breadth without changing the ratio. If an assembly is composed ofwire for instance, the superficial area is the area of a very long solidcylinder whose diameter is that of wire.

I prefer that the size of the cataly t. assemblies be so limited thatthe surface facial ratio is ordinarily less than 50. When coating anassembly with an adherent and rough coating as by electroplating, Iprefer that the assembly being electro- Dlated be so limited that thesurface facial ratio is less than about 20. The electroplate ispreferably heavy, particularly on the faces'nearest the electroplatinganode, and may be applied by a method known to the art, particularlyunder conditions of good throwing power. The current density may beincreased as the electrodeposit thickens and particularly theelectrodeposition may take place at near the highest cathodic currentdensity at which an adherent porous electroplate is'obtained. An exampleof a nickel platin bath is a strong iron free aqueous solution of nickelsulphate together with sufficient minor quantities of boric acid andnickel chloride or ammonium chloride to maintain uniform dissolu- Thenickel is preferably plated on a copper or copper coated iron assembly.

In the preparation of fixed catalyst on metal, especially when preparedon wire or like superflcial forms, I prefer that the metal prior tochemical activation be machined so as to produce burrs or grooves orworked as with heat, and/or alloying to produce fine longitudinalcracks. Similarly sheet metal or stampings are preferably perforated orknurled before assembling. Fixed catalyst, such as a foraminated basemetal or rough inert solid, and whose surfaces comprise nickel or cobaltor silver or like catalytic metal,

or ores or catalytic surfaces accessible to electrolysis and prepared bythe various methods of the art, may be activated or reactivatedaccording to my invention.

The methods and constructions described herein may be used inconjunction with other treatments or otherwise used. For instance theassemblies before or after the chemical treatment given herein may befinally activated as described in my copending application Serial No.117,515 filed December 24, 1936, now U. S. Patent Number 2,191,- 464. Orthe methods described herein may be a used in conjunction with'those ofmy copending application Serial No. 240,007 filed November 8, 1938, nowU. S. Patent Number 2,270,874, as indicated therein. Or anodicallyperoxidized surfaces may be contacted with an aqueous solutioncomprising chromic acid or ammonium molybdate or nickel nitrate. Oranodic peroxidation may be followed by reduction in hydrogen.particularly when the reduced catalyst. is subsequently used for thehydrogenation of unsaturated natural glycerides. After hydrogenatingand/or purifying fatty or like compounds. these compounds or impuritiesmay be extracted, as by refluxing with volatile hydrocarbons. Or morepolar s01- vents such as dichlorethylene or acetone may be used,particularly for a final extraction or when using the catalyst as apurifying agent.

What I claim is:

1. A process for preparing a metallic catalytic surface whose catalyticelement is selected from the class consisting of cobalt, nickel andcopper, comprising activating the surface at the anode in anelectrolytic bath consisting substantially of an aqueous solution of ahydroxide of a metal selected from the class which consists of lithium,calcium, strontium, and barium, thereby forming on the surface ahydrated higher oxide of said catalytic element.

2. A process as described in claim 1, in which the electrolytetemperature and thermodynamic activity coefficient are relatively low.

3. A process for preparing a metallic catalytic surface whose catalyticelement is selected from the class consisting of cobalt, nickel, andcopper, comprising subjecting the surface to an oxidizing treatment andsubsequently further activatin said surface at the anode in anelectrolytic bath consisting substantially of an aqueous solution of ahydroxide selected from the class which consists of lithium, calcium,strontium, and barium, thereby forming on the surface a hydrated higheroxide of said catalytic element.

4. In the art of reactivating a metallic catalytic surface whosecatalytic element is selected from the class consisting of cobalt,nickel, and copper, and which is substantially deactivated in thehydroiining of hydrocarbon distillates containing impurities of organicsulphur compounds, the process comprising reactivating said surface atthe anode in an electrolytic bath consisting substantially of an aqueoussolution of a hydroxide of a metal selected from the class whichconsists of lithium, calcium, strontium, and barium, thereby forming onthe surface a hydrated higher oxide of the catalytic element.

MARION H. GWYNN.

